Investigation Into the Nonlinear Characteristics of a High-Speed Drive Circuit for a Proportional Solenoid Controlled by a PWM Signal

This paper analyzes the unique nonlinear characteristics of a high-speed drive circuit for proportional solenoid, i.e., the inverse discharging drive circuit (IDDC), which has a faster discharging speed than a traditional drive circuit. The experimental results clearly show the piecewise nonlinear relationship between the current and the pulse-width modulation (PWM) duty ratio of the control signal of the IDDC. The mathematical model of the IDDC working processes in one PWM period is constructed in detail to analyze the IDDC nonlinear characteristics. The computational equations of the significant nonlinear features, including the critical PWM duty ratio, the steady-state current, the amplitude of the current oscillation, and the response time of the circuit, are deduced through algebraic analyses, which are verified by a comparison between the experimental and calculated results. These analyses aid the design and control of a solenoid drive circuit for a hydraulic proportional valve. Finally, a modified PI controller that considers the nonlinear characteristics of the IDDC is designed, and the experimental results show that the designed controller significantly improves the response speed of the solenoid current.